364 BOTANICAL GAZETTE [MAY 
(18) found that in cotton cigarettes impregnated with nitrates 
much of the nitrate nitrogen was reduced to ammonia nitrogen. 
Such reductions likely occur to a much slighter degree under better 
conditions of aeration. Similar conditions may hold for hydrogen 
sulphide. 
V. General considerations 
In the destructive distillation gases from carbon compounds, 
whether we consider smoke or illuminating gas, the preponderant 
toxicity of the heavy hydrocarbons, especially ethylene, is very 
interesting. The present paper shows this relation to hold for 
the sweet pea epicotyl, while a former paper pointed out the same 
situation for the carnation flower. Mr. E. M. Harvey of this 
laboratory has shown that the ethylene in illuminating gas deter- 
mines the toxic limit of that mixture to the roots of Vicia Faba, 
though in this case the magnitude of toxicity is much less than in 
the cases of the two plant organs mentioned above. In the light 
of the facts set forth in this paper, it becomes probable that the 
extreme toxicity of smoke for seedlings observed by MOLIscH (22) 
can be attributed to the heavy hydrocarbons. It is as yet un- 
answered whether the nocuous character of smoke to various micro- 
organisms, and to the organs of mature angiosperms as observed 
by this writer, is due to the same constituent. Whatever be the 
case, it is clear that some plants are quite resistant to the destruc- 
tive distillation gases of carbon compounds, as Moriscu states and 
as RicHARDS and MacpouGat (31) have found. To what degree 
the resistance is due to protective structure or permeability char- 
acters and to what degree to peculiarities of the plasma cannot be 
stated. 
It is probable that production of the toxic materials from 
carbon compounds begins considerably before the lower tempera- 
ture limit set for destructive distillation is reached. In soils it 
was found in this laboratory that heating but slightly above go” C. 
for an hour liberated substances that produced the “triple response” 
in the pea epicotyl. Mr. Harvey is now making a study of the 
gases liberated from soils when heated at various temperatures. 
It is evident that contact of hot steam pipes with soil in greenhouses 
